6.4-stable review patch. If anyone has any objections, please let me know.
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From: Waiman Long longman@redhat.com
[ Upstream commit f5063e8948dad7f31adb007284a5d5038ae31bb8 ]
Running the refscale test occasionally crashes the kernel with the following error:
[ 8569.952896] BUG: unable to handle page fault for address: ffffffffffffffe8 [ 8569.952900] #PF: supervisor read access in kernel mode [ 8569.952902] #PF: error_code(0x0000) - not-present page [ 8569.952904] PGD c4b048067 P4D c4b049067 PUD c4b04b067 PMD 0 [ 8569.952910] Oops: 0000 [#1] PREEMPT_RT SMP NOPTI [ 8569.952916] Hardware name: Dell Inc. PowerEdge R750/0WMWCR, BIOS 1.2.4 05/28/2021 [ 8569.952917] RIP: 0010:prepare_to_wait_event+0x101/0x190 : [ 8569.952940] Call Trace: [ 8569.952941] <TASK> [ 8569.952944] ref_scale_reader+0x380/0x4a0 [refscale] [ 8569.952959] kthread+0x10e/0x130 [ 8569.952966] ret_from_fork+0x1f/0x30 [ 8569.952973] </TASK>
The likely cause is that init_waitqueue_head() is called after the call to the torture_create_kthread() function that creates the ref_scale_reader kthread. Although this init_waitqueue_head() call will very likely complete before this kthread is created and starts running, it is possible that the calling kthread will be delayed between the calls to torture_create_kthread() and init_waitqueue_head(). In this case, the new kthread will use the waitqueue head before it is properly initialized, which is not good for the kernel's health and well-being.
The above crash happened here:
static inline void __add_wait_queue(...) { : if (!(wq->flags & WQ_FLAG_PRIORITY)) <=== Crash here
The offset of flags from list_head entry in wait_queue_entry is -0x18. If reader_tasks[i].wq.head.next is NULL as allocated reader_task structure is zero initialized, the instruction will try to access address 0xffffffffffffffe8, which is exactly the fault address listed above.
This commit therefore invokes init_waitqueue_head() before creating the kthread.
Fixes: 653ed64b01dc ("refperf: Add a test to measure performance of read-side synchronization") Signed-off-by: Waiman Long longman@redhat.com Reviewed-by: Qiuxu Zhuo qiuxu.zhuo@intel.com Reviewed-by: Davidlohr Bueso dave@stgolabs.net Acked-by: Joel Fernandes (Google) joel@joelfernandes.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/rcu/refscale.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c index 1970ce5f22d40..71d138573856f 100644 --- a/kernel/rcu/refscale.c +++ b/kernel/rcu/refscale.c @@ -1107,12 +1107,11 @@ ref_scale_init(void) VERBOSE_SCALEOUT("Starting %d reader threads", nreaders);
for (i = 0; i < nreaders; i++) { + init_waitqueue_head(&reader_tasks[i].wq); firsterr = torture_create_kthread(ref_scale_reader, (void *)i, reader_tasks[i].task); if (torture_init_error(firsterr)) goto unwind; - - init_waitqueue_head(&(reader_tasks[i].wq)); }
// Main Task